Marine Mammal Stranding Network

When a marine mammal washes ashore, the forensic investigation begins. How did the animal become stranded? What can it teach us about the health of its ocean habitat? As a member of the Marine Mammal Stranding Network, a federal rescue and research program led by the National Marine Fisheries Service, the Academy responds to strandings along our coast to better understand why the animals washed ashore—and help reduce the frequency of such events in the future.

From Año Nuevo in the south to mid-Mendocino in the north, whenever a deceased marine mammal is reported, responders from the Academy’s Department of Ornithology and Mammalogy spring into action. They locate the specimen, take measurements, and depending on the condition of the animal perform an examination known as a necropsy (or animal autopsy) to collect tissue and bone samples that help determine the animal’s cause of death. After being processed, these samples are added to the Academy’s scientific collection, providing data for researchers from around the world seeking to better understand and protect our ocean’s increasingly vulnerable marine mammals.

It is illegal to approach or handle a sick or injured marine mammal or collect any parts of dead marine mammals. If you encounter a sick or injured marine mammal, call The Marine Mammal Center at 415-289-SEAL. If you encounter a dead marine mammal, call the Academy at 415-379-5381 or email marinemammals@calacademy.org. For more information, view the FAQ below.

In an average year, an estimated four to five gray whales are expected to wash ashore in the Bay Area. Yet starting in 2019, scientists reported an uptick in strandings along the entire Pacific coast of North America. These events led the National Oceanic and Atmospheric Administration (NOAA) to declare the mass die-off an unusual mortality event (UME) and launch a formal investigation into the cause.

At the end of 2023, the investigation concluded after the Pacific gray whale stranding rate decreased. As one of the investigation's state representatives, Academy Senior Collections Manager Moe Flannery spent years leading efforts to collect data from Northern California strandings to determine cause of death and, ultimately, what could be done to protect the beleaguered species.

By closely analyzing all 690 gray whale strandings and subsequent necropsies that occurred during the investigation, the broader team of scientists found that malnutrition was a common cause of death, in addition to mortalities caused by predation, entanglement, and vessel strikes.

It’s not only gray whales that the Academy is helping to protect. In 2015, after a notable uptick in the number of threatened Guadalupe fur seals washing up onto Bay Area beaches, the Academy response team alerted NOAA who declared a UME for the species, thus mobilizing additional resources to investigate the strandings.

Similar efforts in the past from the Academy and other members of the Marine Mammal Stranding Network have successfully led to policy changes in San Francisco Bay, although more research and advocacy is needed.

From getting to the scene to dissecting the mammal to cataloging the samples, conducting necropsies is grueling work. But the trove of information they provide for scientists is an invaluable resource for understanding and protecting marine mammal species.

A general whale necropsy performed by the Academy and The Marine Mammal Center includes the following steps:

1. Evaluate the external state of the animal to look for signs of injury such as lacerations or missing parts.
2. Extract tissue and bone samples by cutting into the animal to assess life history, age, and health. For example, teeth or baleen—a comb-like structure some whales use to filter-feed—can be used to determine the age of the animal and fractured bones can be evidence of blunt force trauma, often from being struck by a boat.
3. Process samples of the animal. Smaller bones are typically treated by maceration—a process that involves soaking them in water where bacteria break down any remaining tissue. Larger bones are placed on the Academy's Living Roof where they are “cleaned” by bacteria in the soil and the Sun’s ultraviolet radiation.
4. Add samples to the Academy’s collections so scientific researchers around the world can analyze them to identify toxins in the animal’s body and diet, when the animal last gave birth, its stress levels, and more.

While seeing whales along the coastline of the Bay Area is an awe-inspiring spectacle, their presence so close to shore sometimes leads to unintentional run-ins with another common sea sighting: ships and vessels.

Each year, a number of whales wash up throughout the Bay Area showing signs of trauma that indicate the cetacean was struck by a vessel. These vessel strikes often occur when a whale surfaces to breathe at the same time a ship passes by. Reducing speeds on the water or adjusting shipping lanes could help prevent these tragic accidents.

Scientists—with help from the public—have been tracking whales and vessel strikes along the coast to get a better idea of where those preventive measures could be most effective, and have already influenced policy changes in the waters surrounding San Francisco Bay.

"My hope is that our research will continue to inform policies like the 2013 changes in shipping lanes and the reduction of boat speeds to protect the iconic, yet vulnerable whales along the California coast." —Moe Flannery, Academy biologist